VALVE COVER GASKET

I have had to have my valve cover gasket redone 3 times! The dealer is not sealing it properly and I keep getting oil all over my engine. Question is what other damage can occur to my engine and its other parts since this has happened 3 times. What should I ask for them to also address. My 10 years on my warranty is almost up and would like to know. So done right this time.
Thank you,
hildacincy